The present invention relates to a system for controlling speed of an automotive engine having an electronic fuel-injection system, and more particularly, to a control system operative during the idling of the automotive engine.
In an idle speed control system for a vehicle having an air-conditioner, the idle speed of an engine must be increased when the air-conditioner is operated. In order to control the idle speed of the engine during the operation of the air-conditioner, a bypass having an auxiliary air valve is provided around a throttle valve of the engine. The auxiliary air valve is opened, when an air-conditioner switch is turned on for operating the air-conditioner. Thus, the amount of intake air increases, the increase of which is detected by an air-flow meter. In response to the increase of intake air, the fuel injection system operates to increase the fuel, thereby increasing the engine idle speed.
However, since the air-flow meter is disposed upstream and far from the auxiliary air valve, the increase of intake air is detected after considerable amount of air has passed the air-flow meter. Accordingly, the increase of fuel is retarded.
As shown in FIG. 5, the idle speed is controlled to keep 700 rpm, the air-fuel ratio at which is about 14.7 (stoichiometric air-fuel ratio). When the air conditioner switch is turned on, the air-fuel mixture is temporarily diluted so that engine speed drops to about 500 rpm. The engine speed reaches a higher idle speed of 850 rpm with a delay. Therefore, the engine idle speed becomes irregular because of an increase of load at a decrease of idle speed.
Japanese Patent Laid Open 58-5438 discloses an engine speed control system for increasing the amount of fuel at starting of a vehicle in order to improve starting characteristic of the vehicle. However, the system is not available for resolving the above problems.